Radio receiver



Patented Oct. 8, 1940 I g r UNITED STATES PATENT OFFICE RADIO RECEIVER Eugene W. Masters, Chicago, IlL, assignor to Electrical Research Laboratories Inc., Chicago, =Ill., a corporationof Illinois Original application May 21, 1938, Serial No. 209,170. Divided and this application Janna 9, 1939, Serial No. 249,933-

.9 Claims. (c1. 179-171) This invention relates to a'ra'dio receiver and a wire M; a condenser 26' is connected between more particularly to a tone control circuit for the wire I 8 and the input lead S2 and shunts the the receiver. upper one-half of the potentiometer l2. The re- It'is :an object :of applicants invention to prosistor or potentiometer 22, which is of the same 5 vide ;a continuously variable tone control and order of magnitude as the potentiometer I2, is bass-boost by which the selectivity of the audiosimilarly provided with a midtap 2d grounded amplifier may be'varied from a normal frequency by the wire 25. One end of the potentiometer 22 reproduction at one end of the tone control to is connected by a wire 28 and a series resistor 3d bass-'iboost in center position and to high freto the wire 18. A high frequency by-pass conquency cut-off at the other end of the range of denser 32 is connected between the wires 26 and 10 tone control. 28 and shunts the left-half of the potentiometer Tone control circuits with which applicant is 22. The adjustable blade or wiper 33 of the familiar are relatively expensive and provide potentiometer 22 is grounded as at'34l. The other merely an adjustable means for cutting out or end of the potentiometer is connected by a wire 7 l5 by-passing from the signal circuits difierent pro- Elli, a high frequency by-pass condenser '38, and

portions of the-highfrequency currents and altera wire 40 to the plate 52 of the tube lil.

natively boosting different "proportions oi the The cathode 4 51 of the tube ii! is heated from lowerfrequency currents. the usual source (not shown) and is grounded it is accordingly an object of applicants inas at 16, or otherwise connected to the other.

vention to provide a continuously variable tone grounded points of the circuits shown. Plate y'o control by -which the tone characteristics of the current is supplied to the tube H! in the usual receiver may be'vari'ed from-ioneendof theaudi0- manner, as for example, through the choke 68 frequency range to the other, .said control'circuit connected to the positive terminal 5% and to the being inexpensive and relatively simple in charplate -42. Output leads 0 and O ,in which a act'er as compared with the prior art. coupling condenser 52 is inserted, connect the 25 More specifically, it is an object of applicants output of the audio-amplifier it to the inputoi a invention toprovide :a combination tone control second stage of audio-amplification or to the inof the variable type providing means for s-i-mulput of a power amplifier. taneously boosting the bass notes and :attenuat- The operation of the circuit is' substantially as ing the high notes in varying proportions under follows. As the adjustable wiper '33 of the 30 the control of a single adjustable resistor unit. potentiometer 22 is m ved to e right toward the Other and further objects and advantages of midtap 2d, the impedance of the parallel circuit, the invention will be apparent from th f 1-1 including the lower half of the potentiometer I2, i-ng description when taken in connection with the resistance 30 and the port on f t .25 the accompanying drawing showing a schematic potentiometer 22 between the adjustable tap and diagram of .a tone control circuit constructed in the Wire 28, increases. For the currents of the accordance with the invention. higher frequencies, the by-pass condenser 32 oi- Th present application i d ii -1; th fe-rs a path of much less impedance than the imapplication filed by William J. Schnell and pedaf any u stant portion of the p 40 Eugene W..Masters, as Serial No. 209,170, on May tiometer between the tap 33 and the wire 28;

21, 1938. hence as the tap 33 is moved to the right toward The single figure of the drawing illustrates a the nt r ap 2 he hi h freq y currents continuously variable tone control by which the try-p d a ll e 10Wel ha f the potentone characteristics of the receiver may be pretiometer I2 and the potentiometer 22 will be cisely adjusted as desired. As shown in this substantially unaffected, The impedance of the 4 drawing, the thermionic tube iii, which may 0011- condenser '32 to the :signalingcurrents of lower or istitute the first stage of audiwamplification in bass frequencies, is relatively high as compared the radio receiver, receives its audio-signal input to the impedance of the potentiometer 22 beth-rough the input leads S! and $2, the lead SI tween the tap 33 and the wire 28. Consequent- .50 being preferably grounded. The lead S2 is conly, as the'wiper 3S5 ismoved to the right toward nected to the lead Si or to ground by a resistor or the center tap it, the voltage drop across thepotentiometer i2 and a control grid M of the lower half of the potentiometer l2, dueto the tube 10 is, connected to the adjustable tap it of signal currents of relatively low or bass fre-' the resistor or potentiometer 12. The .potentiomguencies, will be increased. .55 .eter I2 is tapped substantially at its midpoint by Whe th i er 33 i t th kit-h d d f currents.

the potentiometer 22, the condenser 32 is shunted out and the relatively small resistor 30 constitutes the total resistance in parallel to the lower half of the potentiometer l2. Consequently, the signal voltages impressed upon the tube ID are substantially determined by the upper half of the potentiometer I2 and specifically that portion of the potentiometer which is between the adjustable tap l6 and the midtap of the potentiometer.

The condenser 2!] permits a normal by-passing of the predominantly stronger, higher frequency As the wiper 33 of the potentiometer '22 is moved to the right from the center tap 24 toward the wire 36, the impedance of the input circuit to the currents of different frequencies remains unchanged, since the center tap of the potentiometer is directly connected to ground. However, the impedance of the by-pass circuit connected to the output circuit of the tube l0 constantly decreases as the wiper 33 approaches the end of the potentiometer connected to the wire 36 and therefore more and more of the higher frequency currents are by-passed out of the output circuits. When the wiper 33 engages the right-hand end of the potentiometer 22, the impedance of this high frequency by-pass circuit is a minimum and accordingly the condenser 38 acts to cut off the higher frequencies. The value of this condenser, however, is such as to offer considerable impedance to the lower or base frequencies and hence said frequencies are properly transmitted by the output circuit to the succeeding stage of amplification.

The adjustable tap I6 of the potentiometer I2 may be employed if desired as a volume control, although it has to some slight extent a tone controlling effect. It will therefore be seen that the circuit illustrated in the drawing provides a continuously variable tone control whereby high frequency cut-off is obtained simultaneously with the boosting of the lower or bass frequency, thereby giving a brilliant tone effect and that the circuit further provides a smooth control of tone from normal at one end to bassboost in the center and to high cut-off at the other end or limit of movement of the adjusting device.

In one actual installation made in accordance with the invention, the circuit elements had the following values: Resistors l2 and 22 were each a two-megohm, conventional volume control resistor; resistor 30 had a resistance of 75,000 ohms; the condenser 20 had a capacity of .00025 microfarad; the condenser 32 had a capacity of .003 microfarad; and the condenser 38 had a capacity of .005 microfarad.

Changes may be made in the form, construction and arrangement of the parts without departing from the spirit of the invention or sacrificing any of its attendant advantages, and the right is hereby reserved to make all such changes as fairly fall within the scope of the following claims.

The invention is hereby claimed as follows:

1. In a radio receiver, an audio amplifier having an input circuit, an output circuit, and tone control means in said input circuit, said control means comprising an input control impedance across which audio signal voltages are impressed, a second impedance in shunt to a portion of said first impedance, a capacitance across a portion of said second impedance for by-passing the higher audio frequency currents from said second impedance, and means for varying the effective value of said second impedance to vary the parallel impedance of the shunted portion of the control impedance and the second impedance whereby to vary the response of said amplifier to the currents of lower or bass audio frequencies while maintaining the response of the amplifier to currents of the higher audio frequencies substantially unaffected.

2. In a radio receiver comprising an audio amplifier having an input circuit, and tone control means in said input circuit, said means comprising an input control resistor across which audio signal voltages are impressed, a second resistor and a high audio frequency by-pass condenser connected in shunt to a portion of said second resistor, and a variable connection between. said second resistor and one end of said input control resistor for continuously varying the value of the portion of said second resistor in shunt to the input resistor whereby to boost the bass audio frequencies as the variable connection increases the value of the portion of the second resistor in shunt to the first resistor.

3. In a radio receiver or the like, an audio amplifier having an input circuit and an output circuit, an impedance in said input circuit across which signal voltages are impressed, and a tone control circuit comprising a second impedance having a portion shunting a portion of said first impedance and a portion in said output circuit, a capacity shunting a portion of said second impedance and impedance adjusting means continuously adjustable along said second impedance for varying the value of the impedance in the capacity shunted portion thereof to adjustably control the boosting of the lower or bass audio frequencies while maintaining the higher audio frequencies substantially unaffected as the adjusting means is adjusted through a portion of its range of adjustment and for varying the value of the impedance not shunted by the capacity to adjustably control the dissipation of the higher audio frequencies while maintaining the lower or bass audio frequencies substantially unaffected as the adjusting means is adjusted through another portion of its range of adjustment.

4. In a radio receiver or the like, an audio amplifier having an input circuit and an output circuit, an impedance in said input circuit across which signal voltages are impressed, and a tone control circuit comprising an impedance network for boosting the signal voltages of the lower or bass audio frequencies and dissipating the higher audio frequencies, said impedance network having a portion of predetermined fixed value in said input circuit and another portion of predetermined fixed value in said output circuit, and continuously adjustable means for varying the value of the portion in said input circuit when adjusted through a portion of its range of adjustment and for varying the value of the portion in said output circuit when adjusted through another portion of its range of adjustment, whereby the response characteristic of the input circuit may be varied as said adjustable means is adjusted through a portion of its range of adjustment and the response characteristic of the output circuit may be varied as the adjustable means is adjusted through another portion of its range of adjustment. I

5. In a radio receiver, an audio-amplifier comprising a thermionic tube having a cathode, a grid and a plate, an input control resistor, across which signal voltages are impressed, connected at one end to said cathode, a connection between said resistor and said grid, tone control means connected between said control resistor, said cathode and plate, said tone control means comprising a potentiometer having the wiper thereof connected to said cathode and one end connected to an intermediate point on said input resistor, a high frequency by-pass condenser connected between said plate and the other end of said potentiometer and a high frequency by-pass condenser connected in shunt to a portion of said potentiometer and to said cathode.

6. In a radio receiver or the like, an audio amplifier having an input circuit and an output circult, an impedance in said input circuit across which signal voltages are impressed, a tone control circuit comprising an impedance network of capacity and resistance for boosting the signal voltages of the lower or bass audio frequencies and dissipating the currents of the higher audio frequencies, said network having capacity and resistance portions of predetermined fixed value in said input circuit and another resistance portion of predetermined fixed value in said output circuit and continuously adjustable shunting means for varying the value of the resistance portion in said input circuit when adjusted through a portion of its range of adjustment and varying the value of the resistance portion in said output circuit when adjusted through another portion of its range of adjustment whereby the response characteristic of the input circuit to lower or bass audio frequencies may be varied while maintaining the currents of higher audio frequencies substantially unaffected as the adjustable means is adjusted through a portion of its range of adjustment and the response characteristic of the output circuit to the higher audio frequencies may be varied while maintaining the currents of lower or bass audio frequencies substantially unaffected as the adjustable means is adjusted through another portion of its range of adjustment.

'7. In combination, a thermionic amplifier tube having grid plate and cathode electrodes, an input circuit having an impedance connected between said grid and cathode electrodes and across which impedance signal voltages are impressed, an output circuit connected between the plate and cathode electrodes, a second impedance connected to said first impedance and connected to one of said grid and cathode electrodes, a capacity connected across a portion of said second impedance for by-passing the higher audio frequencies from said second impedance, and an adjustable impedance shunting connection from said second impedance to the connection of said second impedance to the said one of the grid and cathode electrodes for varying the response of said amplifier tube to the currents of lower or bass frequencies while maintaining the response of the amplifier tube to currents of higher audio frequency substantially unaffected.

8. In combination, a thermionic amplifier tube having grid plate and cathode electrodes, an input circuit having an impedance connected between said grid and cathode electrodes and across which impedance signal voltages are impressed, an output circuit connected between the plate and cathode electrodes, a second impedance connected to said first impedance and connected to one of said grid and cathode electrodes, a capacity connected across a portion of said second impedance for by-passing the higher audio frequencies from said second impedance, a second capacity connected between said second impedance and said plate electrode, and a continuously adjustable impedance shunting connection from said second impedance to said first impedance and to said cathode electrode for varying the response characteristic of the input circuit to lower or bass audio frequencies while maintaining the response of the input circuit to higher audio frequencies substantially unaffected as the adjustable impedance shunting connection is adjusted through one portion of its range of adjustment and for varying the response characteristic of the output circuit to the higher audio frequencies while maintaining the response characteristic of the input circuit to lower or bass audio frequencies substantially unaffected as the adjustable impedance shunting connection is adjusted through another portion of its range of adjustment.

9. In combination, an audio amplifier comprising a thermionic tube having a cathode, a grid and a plate, an input control impedance across which signal voltages are impressed, said input impedance being connected between said grid and cathode, tone control means connected between said control impedance, said cathode and said plate, said tone control means comprising a voltage divider having the adjustable connection thereof connected to said cathode, one side of the voltage divider being connected to an intermediate point on said input impedance, a high frequency by-pass condenser connected between said plate and the other side of said voltage divider and to said cathode.

EUGENE W. MASTERS. 

